Are Muawiyah's fighting of Ali and his killing of Hujr ibn Adi considered sins, transgressions, and major sins, and is it preferable for common people to remain silent when delving into such discussions?

The fighting that occurred among the Companions was a result of their ijtihad (independent reasoning). It is obligatory to refrain from discussing their disputes, to love them, to praise them, and not to disparage any of them, while knowing that they were not infallible. Any error they committed was due to ijtihad and is forgiven, Insha'Allah (God willing).

Ahl al-Sunnah wal Jama'ah (the People of the Sunnah and the Community) believe that the fighting that took place among the Companions does not fall under the threats mentioned in the Prophetic traditions. Rather, they were mujtahids (those who perform ijtihad) who interpreted matters, and they did not intend disobedience or mere worldly gain. Instead, each group believed they were in the right.

The summary of the Ahl al-Sunnah's methodology is: purity of hearts and tongues towards the Companions, love for the Prophet's family (peace be upon him), disavowal of the Rawafid (Shi'a) and the Nawasib (those who harbor animosity towards Ali), refraining from delving into the disputes that occurred among the Companions, while acknowledging that what is narrated about their shortcomings is either false, exaggerated, distorted, or that they are excused for what is true.

They were either mujtahids who were correct, for whom there are two rewards, or mujtahids who erred, for whom there is one reward, and their error is forgiven. This is while acknowledging their lack of infallibility from sins. However, they have prior merits and virtues that necessitate the forgiveness of any misdeeds that might emanate from them, and it has been established that they are the best of generations.